High molecular weight polyamides, i.e. nylon, are prepared by polymerization of a dinitrile, a diamine and water in the presence of a dicarboxylic acid.
Commercial processes for preparing nylons, which use diamines and dicarboxylic acids as raw materials are well known in the art. The commercial reaction may be represented by the following formula: EQU H.sub.2 NR"NH.sub.2 +HOOCRCOOH.fwdarw.NR"NHOCRCO.sub.x +2H.sub.2 O
wherein R and R' are generally hydrocarbon groups. At an early date in the development of nylons it was proposed that linear polyamides be made by heating a reaction mixture comprising a dinitrile, a diamine and water, as disclosed in Greenwalt, U.S. Pat. No. 2,245,129. The procedure disclosed in the Greenwalt patent is carried out in two stages, the first stage comprising the heating of the reaction mixture in the closed reaction vessel until a low molecular weight polyamide is formed, and the second stage comprising subsequent heating of the precursor thus produced to form a higher molecular weight polyamide. Later patents, such as U.S. Pat. No. 3,847,876 provide for an improved process for preparing polyamides by contacting the dinitrile, diamine and water in the presence of ammonia. The polyamides thus produced, however, were, by commercial standards, of relatively poor quality and of only intermediate molecular weight and, the commercial development of processes for the preparation of nylons, such as nylon-6,6 has followed the diamine-dicarboxylic acid route described above.
It is an object of the present invention to provide an improved process for preparing high molecular weight polyamides directly from diamines and dinitriles. It is a further object of this invention to provide a process for producing nylon-6,6 from hexamethylene diamine and adiponitrile.